The rumor of the day is that Google is looking to spend as much as $6 billion to buy Groupon, a service that offers local deals.

If Google pays anywhere near that, it might be the nuttiest tech acquisition ever.

A little perspective: Google paid $1.6 billion for YouTube, the biggest video site on the web. It paid $750 million for AdMob, the largest mobile advertising company. It spent $3.1 billion for DoubleClick, the largest display advertising firm. If Groupon fetched $6 billion, it would be far more than any of those.

And what would Google get for the money?

A two-year-old company that’s said to be doing $50 million a month in revenue. It serves more than 150 markets in North America and 100 outside that. Groupon makes money by offering subscribers just one local deal each day, contingent on enough people signing up for it.

It’s a nice concept, and if Groupon has been pulling in $50 million in recent months, that’s impressive for such a young company. But here’s the problem: I have a hard time seeing any significant intellectual property Groupon has created here. I have a hard time discerning any significant barriers to entry that would keep a company like Facebook from coming in and eating Groupon’s lunch. And I have a really hard time seeing how the Groupon concept model as it now exists will scale.